1. Field of the Invention
The present invention is generally directed to a flexible circuit electrode array especially for biomedical implants, especially implantable medical devices, such as retinal prosthesis and a method of manufacturing the flexible circuit electrode array.
2. Description of the Related Art
In U.S. Pat. No. 3,699,970 “Striate Cortex Stimulator” to Giles Skey Brindley et al. an implantable device is disclosed comprising a plurality of electrodes for stimulating the striate cortex.
In U.S. Pat. No. 4,487,652 “Slope Etch of Polyimide” to Carl W. Amgren a semiconductor having an insulating layer overlying a metal layer is disclosed, wherein the insulator comprises an upper oxide layer, an intermediate polyimide layer, and a lower oxide layer in contact with the metal layer, a method for etching a via from an upper surface of the polyimide layer to the metal layer comprising the steps of applying photoresist; etching an opening from an upper surface of the photoresist layer to the upper oxide layer at a location for forming the via so that an upper surface of the upper oxide layer is exposed at the via location; heating the photoresist to cause a more gradual slope of the photoresist layer from the upper surface of the upper oxide layer at the via location to the upper surface of the photoresist layer; applying reactive ion etchant with a predetermined selectivity between photoresist and oxide to transfer the slope of the photoresist layer to the upper oxide layer at a predetermined ratio; and applying a reactive ion etchant with a predetermined selectivity between oxide and polyimide to transfer the slope of the upper oxide layer to the polyimide layer at a predetermined ratio, whereby the lower oxide layer is simultaneously etched to expose the metal layer at the via location.
In U.S. Pat. No. 4,573,481 “Implantable Electrode Array” to Leo A. Bullara an electrode assembly for surgical implantation on a nerve of the peripheral nerve system is disclosed.
In U.S. Pat. No. 4,628,933 “Method and Apparatus for Visual Prosthesis” to Robin P. Michelson a visual prosthesis for implantation in the eye in the optical pathway thereof is disclosed.
In U.S. Pat. No. 4,837,049 “Method of Making an Electrode Array” to Charles L. Byers et al. a very small electrode array which penetrates nerves for sensing electrical activity therein or to provide electrical stimulation is disclosed.
In U.S. Pat. No. 4,996,629 “Circuit Board with Self-Supporting Connection Between Sides” to Robert A. Christiansen et al. a copper supporting sheet is disclosed having vias for connecting semiconductor chips to surface mount components. A laminate of polyimide has vias corresponding to the supporting layer vias with copper covering those vias.
In U.S. Pat. No. 5,108,819 “Thin Film Electrical Component” to James W. Heller a thin film electrical component is disclosed comprising a rigid glass carrier plate, a substrate bonded to the rigid glass carrier plate, the substrate comprising a polyimide establishing a bond with the rigid glass carrier plate that is broken upon immersion of the substrate and the rigid glass carrier plate in one of a hot water bath and a warm temperature physiologic saline bath to release the polymer from attachment to the rigid glass carrier plate, and means for providing an electrical circuit, the providing means being bonded to the substrate and undisrupted during release of the substrate from attachment to the rigid glass carrier plate.
In U.S. Pat. No. 5,109,844 “Retinal Microstimulation” to Eugene de Juan Jr. et al. a method for stimulating a retinal ganglion cell in a retina without penetrating the retinal basement membrane at the surface of the retina is disclosed.
In U.S. Pat. No. 5,178,957 “Noble Metal-Polymer Composites and Flexible Thin-Film Conductors Prepared Therefrom” to Vasant V. Kolpe a composite article is disclosed comprising a polymeric support selected from the group consisting of a polyimide, polyethylene terephthalate, and polyester-ether block copolymer having a noble metal deposited directly onto at least one surface, wherein said deposited metal exhibits a peel force of at least about 0.05 kg per millimeter width after 24 hour boiling saline treatment.
In U.S. Pat. No. 5,215,088 “Three-Dimensional Electrode Device” to Richard A. Norman et al. a three-dimensional electrode device for placing electrodes in close proximity to cell lying at least about 1000 microns below a tissue surface is disclosed.
In U.S. Pat. No. 5,935,155 “Visual Prosthesis and Method of Using Same” to Mark S. Humayun et al. a visual prosthesis is disclosed comprising a camera for receiving a visual image and generating a visual signal output, retinal tissue stimulation circuitry adapted to be operatively attached to the user's retina, and wireless communication circuitry for transmitting the visual signal output to the retinal tissue stimulation circuitry within the eye.
In U.S. Pat. No. 6,071,819 “Flexible Skin Incorporating MEMS Technology” to Yu-Chong Tai a method of manufacturing a flexible microelectronic device is disclosed comprising first etching a lower side of a wafer using a first caustic agent; depositing a first layer of aluminum on an upper side of the wafer; patterning the first layer of aluminum; depositing a first layer of polyimide on the upper side of the wafer, covering the first layer of aluminum; depositing a second layer of aluminum on the upper side of the wafer, covering the first layer of polyimide; depositing a second layer of polyimide on the upper side of the wafer, covering the second layer of aluminum; depositing a third layer of aluminum on the lower side of the wafer; patterning the third layer of aluminum; second etching the lower side of the wafer using the third layer of aluminum as a mask and the first layer of aluminum as an etch stop and using a less caustic agent than said first caustic agent, such that the wafer is divided into islands with gaps surrounding each island; and depositing a third layer of polyimide on the lower side of the wafer, such that the gaps are at least partially filled.
In U.S. Pat. No. 6,324,429 “Chronically Implantable Retinal Prosthesis” to Doug Shire et al. an apparatus is disclosed which is in contact with the inner surface of the retina and electrically stimulates at least a portion of the surface of the retina.
In U.S. Pat. No. 6,374,143 “Modiolar Hugging Electrode Array” to Peter G. Berrang et al. a cochlear electrode array for stimulating auditory processes is disclosed.
In U.S. Pat. No. 6,847,847 “Retina Implant Assembly and Methods for Manufacturing the Same” to Wilfried Nisch et al. a retina implant is disclosed comprising a chip in subretinal contact with the retina and a receiver coil for inductively coupling there into electromagnetic energy.
In U.S. Pat. No. 6,970,746 A1, “Microcontact structure for neuroprostheses for implantation on nerve tissue and method therefore” to Rolf Eckmiller et al. a four layer microcontact structure is disclosed in which the active connection between the microcontact structure and the nerve tissue is brought about by electrical stimulation. The layer adjacent to the nerve tissue to be stimulated is composed of the polymer polyimide and contains penetrating electrodes made of platinum which forms the adjoining layer. There follows a further layer of the polyimide and a layer of the polymer polyurethane. Polyurethane has the property of thermal expansion relative to polyimide.
In U.S. Pat. No. 6,976,998 A1 “Minimal Invasive Retinal Prosthesis” to John F. Rizzo et al. a retinal prosthesis is disclosed comprising an RF coil attached to the outside of and moving with an eye to receive power from an external power source; electronic circuitry attached to and moving with the eye and electrically connected to the RF coil; a light sensitive array electrically connected to the electronic circuitry and located within the eye for receiving incident light and for generating an electrical signal in response to the incident light; and a stimulating array abutting a retina of the eye and electrically connected to the electronic circuitry to stimulate retinal tissue in response to the electrical signal from the light sensitive array. A supporting silicone substrate has a polyimide layer spun onto its surface and cured. The copper or chrome/gold conducting layer is then added and patterned using wet chemical etching or a photoresist lift-off process. Next, a second polyimide layer is spun on, and the regions where circuit components are to be added are exposed by selective dry etching or laser ablation of the upper polyimide layer in the desired areas. Finally, the completed components are removed from their supporting substrate.
Polyimide, also known as PI, has been mass-produced since 1955. It is used in bearing materials, thrust washers, and semiconductor wafer clamps. It has high impact and dielectric strength, high heat resistance and a low coefficient of thermal expansion and excellent mechanical, thermal, and electrical properties. Polyimide is typically applied in liquid form, and then thermally cured into a film or layer with the desired properties. The film can be patterned using photographic or other processes. Microelectronic applications include stress buffer, passivation layer, chip bonding, and interlayer dielectric.
Eugene de Juan Jr. et al. at Duke University Eye Center inserted retinal tacks into retinas in an effort to reattach retinas that had detached from the underlying choroid, which is the source of blood supply for the outer retina and thus the photoreceptors. See for example E. de Juan Jr., et al., “Retinal tacks”, Am J. Ophthalmol. 1985 Mar. 15; 99 (3):272-4.
Hansjoerg Beutel et al. at the Fraunhofer Institute for Biomedical Engineering IBMT demonstrated the bonding of a gold ball by force, temperature, and ultrasound onto an aluminum metal layer. See for example Hansjoerg Beutel, Thomas Stieglitz, Joerg-Uwe Meyer: “Versatile Microflex-Based Interconnection Technique,” Proc. SPIE Conf. on Smart Electronics and MEMS, San Diego, Cal., March 1998, vol. 3328, pp 174-182. A robust bond can be achieved in this way. However, encapsulation proves difficult to effectively implement with this method. Gold, while biocompatible, is not completely stable under the conditions present in an implant device since it dissolves by electromigration when implanted in living tissue and subject to an electric current. See for example Marcel Pourbaix: “Atlas of Electrochemical Equilibria in Aqueous Solutions”, National Association of Corrosion Engineers, Houston, 1974, pp 399-405.
A system for retinal stimulation comprising a polyimide-based electrodes being coated with platinum black are described by Andreas Schneider and Thomas Stieglitz. See for example Andreas Schneider, Thomas Stieglitz: “Implantable Flexible Electrodes for Functional Electrical Stimulation”, Medical Device Technology, 2004.
A process for activating a base polyimide layer prior to applying a top polyimide layer is described by Balasubrahmanyan Ganesh, who suggests to clean, roughen, and oxygenate the base polyimide by using reactive ion etching (RIE) in oxygen plasma for 10 s at 50 W, and 800 mTorr pressure in an Oxford Plasmalab-80 Plus system. The top polyimide layer is then spun-on immediately after the plasma after the plasma roughening and the wafer is set aside for 45 min. See for example Balasubrahmanyan Ganesh: “A Polyimide Ribbon Cable for Neural Recording and Stimulation Systems”, a Thesis for the Degree of Master of Science, Department of Materials Science and Engineering, The University of Utah, March 1998.
A process for activating a base polyimide layer prior to applying a top polyimide layer is described by Nancy Stoffel, Crystal Zhang and Edward J. Kramer. Stoffel et al. suggest using wet chemical treatments to hydrolyze the films according to a method reported by K. W. Lee et al. (1990). Stoffel et al. found solutions of both 1 M KOH and 1 M tetramethyl ammonium hydroxide to be effective for polyimide films. Solutions of 0.2 M HCl and acetic acid were used and found to be effective for converting polyamate salt into a polyamic acid. See for example Nancy Stoffel, Crystal Zhang and Edward J. Kramer: “Adhesion of Polyimide Laminates”, Application of Fracture Mechanics in Electronic Packaging and Materials, ASME, EEP-Vol. 11/MD-Vol. 64, pp. 79-84, 1995.